Conventional cellular communication systems are generally designed for voice services, voice services are based on an assumption that service load scarcely changes (service load is relatively static or changes semi-statically) and the proportions of uplink services and downlink services are also symmetrical, for example, a Frequency Division Duplexing (FDD) system uses paired uplink and downlink frequency spectrums. However, this relatively static assignment of uplink and downlink frequency resources in a Long Term Evolution (LTE) system cannot adapt well to changes of services.
As Mobile Broadband (MBB) services develop rapidly in recent years, the demands for wireless communications increase continuously, and more and more application services show a feature that more downlink services are needed than uplink services and only in some certain scenarios, more uplink services are needed than downlink services. Error! Reference source not found. The uplink-downlink ratios of some typical applications are given below:
TABLE 1Uplink/downlinkService typespeed ratio (average)Online video 1:37Software 1:22downloadingWeb browsing1:9Social network4:1Email1:4P2P video3:1
As shown in Table 1, downlink plays a leading role for online video, software downloading, web browsing and so on, while uplink plays the same role for social network, P2P sharing and so on.
Two duplexing modes are currently available: FDD and Time Division Duplex (TDD), for the FDD, since paired frequency spectrums are needed, resources are not utilized flexibly, moreover in consideration of the asymmetry between uplink and downlink in existing services, downlink plays a leading role in most of services, thus the utilization efficiency of the uplink frequency spectrum is relatively low and a large amount of the uplink frequency spectrum resources are not even used in many cases. For the TDD, as frequency spectrum resources are used in a time division manner, resource utilization for the TDD is higher relative to that for the FDD. To take advantage of the merits of these two duplexing modes with backward compatibility taken into consideration, one of the trends of the future duplexing technologies is fusion of the FDD and the TDD. A duplexing mode called flexible duplex emerges. That is, in a frame structure, some flexible subframes are defined which can be dynamically switched to serve as uplink subframes or downlink subframes, for example, downlink data is transmitted in the FDD uplink frequency spectrum.
In this case, because the downlink transmission is conducted in the FDD uplink frequency spectrum, to ensure the transmission of downlink data, a terminal is needed to feedback HARQ-ACK response information corresponding to the downlink data. At present, however, no related technical solution has been proposed to feedback HARQ-ACK response information in a flexible duplex scenario.